PLEASE HELP!! First to answer correctly gets brainliest

Review the chart to answer the question that follows.
Total Population GDP
Country A 5,000 10,000
Country B 10,000 15,000
Country C 2,000 8,000
Country D 1,000 5,000

Which additional type of data would be most important for comparing the standard of living of these countries?
A. Share of budget set aside for defense
B. Percent of territory that is water
C. Number of airports
D. Literacy rate

I think it is either A or D but I don't know which one!!! PLEASE HELP